Gestational diabetes mellitus (GDM) complicates 3-10% of all pregnancies and is increasing in incidence, yet little is known about the molecular mechanisms of the insulin resistance. It results in significant morbidity to both the mother and the fetus, including a 50% risk of developing type 2 diabetes mellitus in the mother, and a high prevalence of childhood obesity and adult type 2 diabetes in the offspring. This research will examine mechanisms of insulin resistance in mothers with GDM compared to pregnant controls by studying skeletal muscle insulin signaling and mitochondrial function in a longitudinal prospective manner in three groups of subjects. Lean pregnant, obese pregnant, and obese GDM patients will be studied during late pregnancy and again after delivery when diabetes and hyperinsulinemia subsides. Repeat muscle biopsies will be collected at the time of elective cesarean section and again at 6-8 weeks post-partum in order to examine whether or not impairments in insulin signaling and mitochondrial function persist postpartum. We hypothesize that women who continue to have impaired glucose tolerance postpartum will demonstrate a chronic detriment in mitochondrial function and insulin signaling, some features of which will persist in skeletal muscle myotubes in-vitro, allowing us to investigate potential epigenetic mechanisms for increased risk underlying the progression to type 2 diabetes. PUBLIC HEALTH RELEVANCE: The prevalence of obesity and insulin resistance is widespread in the United States, and only increasing. Obese, insulin resistant women are more susceptible to developing gestational diabetes during pregnancy and have greatly increased risk of developing type 2 diabetes post-partum. Mitochondrial dysfunction has been widely implicated in the development of skeletal muscle insulin resistance, although the cellular mechanisms remain unknown. By examining women with and without gestational diabetes during and following delivery, we may be able to more clearly define these mechanisms and their association with insulin resistance. This knowledge will not only provide valuable information regarding the insulin resistance of pregnancy but also the predisposition to type 2 diabetes in women who develop gestational diabetes.